1. Field of the Invention
The invention relates to hybrid power relays used for opening or closing electrical circuits.
2. Discussion of the Background
At the present time there are two main types of relays according to their operating technologiesxe2x80x94electromechanical relays and semiconductor or static relays.
The relays are designed to withstand the current of the electrical circuit into they are inserted and to cut off the electrical circuit under load, that is to say when an electric current flows through the circuit.
Electromechanical-type relays comprise one or more electrical contacts having a mechanical movement, these being coupled to a moveable element of the magnetic circuit of an electromagnet. The electromagnet is actuated by supplying power to its coil, which produces an induction flux in the magnetic circuit which causes the moveable element to move and the electrical contacts of the relay to open or close.
The switching of an electrical circuit under load by an electromechanical relay, and particularly when the circuit is inductive, produces arcs between the contacts at the moment the circuit is opened or closed. This phenomenon is usually called sparking.
Sparking causes carbon to form between the contacts (carbonization) due to the combustion of dust or particles of matter when the arc occurs. One consequence of the carbonizing is the degradation in the quality of the contact owing to the increase in the resistance to the flow of current.
Unlike electromechanical relays, static relays do not use moveable mechanical elements but semiconductor components capable of opening or closing an electrical circuit into which they are inserted. Static relays use semiconductor components such as triacs, thyristors, transistors, MOS-thyristors known as insulated-gate controlled thyristors or IGCTs, insulated-gate bipolar transistors or IGBTs and MOS controlled thyristors or MCTs.
These types of semiconductor components have two power inputs intended to be connected to an electrical circuit and one control input which switches the semiconductor component, when it is inserted into the electrical circuit via its two power inputs, either into an off state or into an on state between these two power inputs. In the off state, the entire voltage of the electrical circuit is applied to the power inputs of the semiconductor component and in the on state the current of the electrical circuit into which the semiconductor is inserted flows through the latter.
However, static relays have a drawback compared with electromechanical relays. This is because, in the on state (or saturated state), the semiconductor component has, between its power inputs, when the current flows, a residual saturation voltage which dissipates thermal energy in the semiconductor component and raises its temperature. In a triac for example, this residual saturation voltage is about 1.5 volts. Consequently, static power relays must be used in conjunction with heat sinks in order to remove the heat energy dissipated by the semiconductor component and thus to ensure that they have a sufficient lifetime.
In another type of relay, commonly called a hybrid relay, the semiconductor component is connected in parallel with the mechanical-movement electrical contact of the electromechanical relay. Actuation of the hybrid relay simultaneously causes the semiconductor component to be turned on, which component absorbs the switching arc, and causes the contact of the relay to close, which short-circuits the semiconductor component. Since the contact has a very low resistance, the current of the electrical circuit flows through the contact and not through the semiconductor component, which is de-energized, thus preventing it from heating up. However, this solution has drawbacks, namely that an increase in the resistance between the contacts of the relay, due to various phenomena such as, for example, carbonizing, oxidation, ageing or a mechanical defect of the contacts, causes the appearance, between the contacts, of a voltage drop which may be high enough to energize the semiconductor component in parallel with the contact and to make some, to see practically all, of the current of the electrical circuit flow permanently through the semiconductor component, which in turn causes its heat-up or indeed its destruction if it is not equipped with a heat sink.
The present invention makes it possible to mitigate the drawbacks of the prior art by providing a hybrid power relay intended to be inserted into an electrical circuit, the hybrid relay comprising an electrical contact having a mechanical movement, a semiconductor component in parallel with the electrical contact having a mechanical movement, control means which cause, on the one hand, the contact to close and turn on the semiconductor component in response to a first control signal and which cause, on the other hand, the contact to open and turn on the semiconductor component in response to a second control signal, characterized in that the control means comprise means:
for generating, on the basis of the first control signal, a contact-make signal;
for generating, on the basis of the first control signal, independently of the make signal, a first signal for turning on the component, starting before the contact has closed and terminating after it has closed;
for generating, on the basis of the second control signal, a contact-break signal;
for generating, on the basis of the second control signal, independently of the break signal, a second signal for turning on the component, starting before the contact has opened and terminating after it has opened.
The hybrid relay according to the invention can operate with any power component, namely triacs, thyristors, but also transistors, IGBTs, IGCTs and MCTs.
The hybrid power relay is produced so as to generate, on the basis of the first relay control signal, the contact-make signal and the first signal for turning on the component, independently of each other, thereby making it possible to turn on the semiconductor component either simultaneously with the contact-make signal or before the contact-make signal. The same applies when opening the contact. One advantage stemming from this functionality is that the reaction time of the mechanical contact, either upon the appearance of the make signal or upon the appearance of the break signal, does not come into play. This is because, in the case of a relay having a rapid response time, the turn-on of the semiconductor component may be triggered upon closure of the contact, before this closure and upon opening of the contact, before this opening, thereby ensuring sufficient time to establish the current in the semiconductor and thus either open or close the contact with an almost zero current.
In the case of a relay having a response time long enough for the current in the semiconductor to be established, the semiconductor component turn-on signal may be transmitted simultaneously with either the relay contact-make signal or the relay contact-break signal.
The hybrid power relay according to the invention ensures synchronized switching between the electrical contact having a mechanical movement and the semiconductor component in parallel with the contact. This synchronization eliminates practically the entire electric arc that can occur when the electrical contact opens or closes. This is because the contact is opened or closed only when the semiconductor component has been put into the on state.
The hybrid power relay according to the invention has the advantage of making it unnecessary to use a heat sink for the semiconductor component, thereby reducing the cost and the size of the hybrid relay.
In fact, after the contact has closed, the stoppage of the first signal for turning on the semiconductor component prevents the latter from being able to be energized by the appearance of a permanent voltage drop at its terminals, due for example to the carbonizing of the contact or to a permanent mechanical fault in the contact, thus preventing the current of the electrical circuit from flowing into the semiconductor component and protecting it from an abnormal heat-up or indeed from a destruction.
Another advantage of stopping the first signal for turning on the semiconductor component, putting it into the off state, after the contact has closed, stems from the fact of forcing the current of the electrical circuit to flow through the contact, thereby cleaning the contact by destroying the particles of carbonized matter due to the carbonizing.